Gravity Lesson 5

Gravity can be used to slingshot spacecraft.
Elliptical transfer orbits can be used for space travel.

When a rocket goes from the Earth to Mars, it follows these steps:

• It starts out on the Earth, orbiting the sun like the Earth does;
• It waits for the right moment, and...
• It lifts off the Earth, burning fuel and changing its solar orbit;
• It runs out of fuel, and drifts along its new trajectory;
• It reaches the orbit of Mars, and lands!

The diagram below shows a Hohmann Transfer Orbit. If we put a ship in this orbit, it could shuttle people and things from the Earth to Mars. We would just "jump off" the Earth when the transfer ship came by, and then "jump off" when it passed by Mars. No fuel required (aside from the "jumps")! You can duplicate this orbital arrangement in the My Solar System simulation from PhET, by giving the Earth an orbital radius of 93 (million miles) and Mars an orbital radius of 140 (million miles), and an elliptical orbit that goes from 93 to 140! Think about how to adjust the masses and the speeds to get the same diagram that you see below!

Create a digital story (written narrative, ComicLife, or QuickTime screencast) related to an imaginary Hohmann transfer trip. Your story, aside from being vivid and interesting, should demonstrate your understanding of circular and elliptical orbits, and how gravity and speed are related for these orbits. You should also point out advantages and disadvantages of the Hohmann transfer orbit.